1. Field of the Invention
The present invention relates to novel N-substituted neuraminic acid derivatives having an excellent immunological activity and processes for preparation thereof.
2. Description of the Prior Art
So far, it has been known in the art that N-substituted neuraminic acids are present in many animals and on the cell surface of several bacterias as a complex of sialic acid such as glycoprotein, glycolipid, oligosaccharide or polysaccharide.
Recently, N-substituted neuraminic acids have become important substances in medicine and pharmaceutics relative to nerve function, cancer, inflammation, immunity, viral infection, differentiation, hormone receptor etc. However, the role of N-substituted neuraminic acids in the complex of sialic acid has not been ascertained yet.
Furthermore, N-substituted neuraminic acids have been studied by many organic chemists and therefore, many kinds of simple derivatives thereof have been obtained. But no derivative having an excellent immunological activity has been obtained yet.
On the other hand, the average span of human life has been extended because of improvements in medical treatment for malignant tumor of hematopoietic organ, many kinds of cancers, and collagen disease. On the other hand, with the great increase in use of medicines, for example, medicines for adrenal cortical hormone or immunosuppresant, a number of undesirable side effects arise together with lowering and decrease in immunological competence.